Pentacyanoethane and its salts



United States Patent 3,144,478 PENTACYANOETHANE AND ITS SALTS Owen Wright Webster, Wilmington, DeL, assignor to E. R. du Pont de Nemonrs and Company, Wilmington, Del.,

a corporation of Delaware No Drawing. Filed Oct. 27, 1960, Ser. No. 65,258 9 Claims. (Cl. 260-4658) This invention is concerned with a new cyanocarbon acid and its salts, and with the process for their preparation.

The discovery of tetracyanoethylene has stimulated the whole field of cyanocarbon chemistry and led to the discovery of many derivatives and related compounds. Illustrative of such compounds are cyanocarbon acids and their salts (Middleton et al., J. Am. Chem. Soc. 80, 2795 (1958)). Examples of these are the sodium and silver salts of cyanoform, as Well as its alcoholate derivatives, which have long been known (Schmidtmann, Ber. 29, ll7l-3 (1896)); 1,1,2,2-tetracyanoethane which has been found to be a strong acid yielding corresponding salts (US. 2,788,356); similarly, l,1,2,3,3-pentacyanopropene which is a strong acid yielding corresponding salts (US. 2,766,243).

There have now been discovered pentacyanoethane and its salts and a process for their preparation by the reaction of an alkali metal cyanide with a molecular excess of tetracyanoethylene.

Pentacyanoethane and the pentacyanoethanide salts in the free state are stable for only limited periods of time. They are best preserved for longer periods by incorporating in them at least 0.01 mole of tetracyanoethylene for each mole of the pentacyanoethane compound. In comparison with other cyanocarbon acids and salts, pentacyanoethane and its salts are unique in that they readily yield cyanogen on heating, particularly in the range from 50-200 C. They are thus convenient sources for the preparation of cyanogen.

In the process of this invention it suffices to bring an alkali metal cyanide into intimate contact with a molecular excess of tetracyanoethylene. The excess of tetracyanoethylene should be at least 0.01 mole. It is essential to the formation of the pentacyanoethanide that tetracyanoethylene be present in molar excess (more moles of tetracyanoethylene than an alkali metal cyanide) to the amount of available alkali metal cyanide at all times during the reaction. Available is meant in the sense that the alkali metal cyanide is accessible to the tetracyanoethylene. That is, where the alkali metal cyanide is substantially insoluble in an inert diluent, only that amount of the alkali metal cyanide which has dissolved or is on the surface of the solid particle is accessible.

It is convenient, though not essential, to carry out the process of this invention in the presence of a liquid diluent which is inert to the reactants and products. This alternative is particularly preferred when it is desired to control the temperature at which the reaction takes place. Suitable diluents include acetonitrile, tetrahydrofuran, ethylene glycol dimethyl ether, tetramethylene sulfone, dimethylformamide, benzonitrile, anisole, and the like.

The temperature at which the process of this invention is carried out may be varied Widely. Temperatures in the range of room temperature and below are preferred and particularly temperatures in the range of 100 to 0 C. At room temperature and above the yield of pentacyanoethanide is reduced by competing reactions, and at temperatures of 50 C. and above the pentacyanoethanide as it is formed is cleaved to yield cyanogen and the corresponding tetracyanoethylenide.

Pressure is not a critical factor in this process, and

3,144,478 Patented Aug. 11, 1964 pressures both above and below atmospheric pressure are operable.

To avoid oxidation of the pentacyanoethanides, it is preferred to carry out the reaction of this invention in the essential absence of molecular oxygen. This may be accomplished by operating in an atmosphere of nitrogen, as in the examples below, by employing other inert gases, such as argon, helium, and the like, by operating under reduced pressure or by other means known in the art.

The products of this invention may be represented by the formula M[C(CN) C(CN) where M is a cation and x is the valence of the cation. Thus, M may be hydrogen, an inorganic cation, or an organic cation. inorganic cations include particularly the ammonium ion and the ions of the metals, i.e., elements with atomic numbers of 34, 1113, 19-32, 3751, 55-84, and 87-101. Organic cations include particularly the substituted ammonium and sulfonium ions.

Pentacyanoethane is obtained from an alkali metal pentacyanoethanide by reaction with an aqueous mineral acid as illustrated in Example II.

Pentacyanoethanides with cations other than hydrogen or the alkali metals are prepared by metathesis from these materials. Pentacyanoethane reacts with metal carbonates to yield the corresponding metal pentacyanoethanides. For example, pentacyanoethane reacts with barium carbonate to yield barium pentacyanoethanide. When calcium carbonate is employed, calcium pentacyanoethanide is obtained. Barium pentacyanoethanide is useful for preparing other salts of pentacyanoethane by reaction with aqueous solutions of sulfates. The barium sulfate which forms as a by-product is precipitated quantitatively and may be removed by filtration, leaving an aqueous solution of the desired pentacyanoethanide which is readily isolated by evaporation of the solution. For example, aqueous solutions containing equivalent amounts of barium pentacyanoethanide and magnesium sulfate are mixed. The barium sulfate which forms is filtered off and magnesium pentacyanoethanide is obtained by evaporation of the filtrate. In a similar manner, aqueous solutions of the sulfates of Al+++, Ce+++, 3 c Ga+++, In+++, Ni Li+, 14+, Mn++, Rb+, Sn++, UO2++, NHU, s 5 3 2 s)2 2 3)s and 3)3 react with barium pentacyanoethanide to yield the corresponding metal, amine, or sulfonium salts of pentacyanoethane.

In the following examples parts are by weight unless otherwise specified.

Example I In a system continuously blanketed with nitrogen a suspension of 10 parts of sodium cyanide in 157 parts of acetonitrile is cooled to 0 C. and 25 parts of tetracyanoethylene is added in one portion. The sodium cyanide dissolves slowly so that a chemical excess of tetracyanoethylene is present in solution substantially throughout the reaction. The mixture is stirred for three hours at 0 C. and then filtered. The filtrate is diluted with 428 parts of diethyl ether and about 390 parts of petroleum ether. The dark oil which separates is with drawn and diluted with an additional 143 parts of diethyl ether. This causes 17 parts of sodium pentacyanoethanide to separate in the form of a tan crystalline precipitate. This is recovered by filtration and dried.

Example II To about 111 parts of 6 N hydrochloric acid at 0 C. is added 2 parts of sodium pentacyanoethanide prepared as in Example 1. After stirring the reaction mixture for about five minutes, the precipitate which forms is separated by filtration. The precipitate is dissolved in ether.

I, ,3 The ether solution is dried over a dehydrated crystalline sodium alumino silicate drying agent (Molecular Sieve 4A from the Linde Co.) and then evaporated to dryness to leave 0.5 part of pentacyanoethane in the form of a crystalline solid. It'is characterized by its infrared absorption spectrum which shows bands at 1265, 1071, 900, and 790 cm.

Example 111 Anal.Calcd. for NaC N C, 47.47; N, 37.55. Found: C, 47.49; N, 40.16.

Example IV A solution of 128 parts of tetracyanoethylene in 1566 parts of dry acetonitrile is treated with 25 parts of dry, powdered sodium cyanide under nitrogen. The darkcolored solution is stirred one-half hour at room temperature and is then diluted with 42,810 parts of dry ether. Sodium pentacyanoethanide, 45 parts, crystallizes from the solution and is identified by its infrared spectrum.

Example V A solution of 227 parts of tetracyanoethylene in 3131 parts of acetonitrile is cooled to 40 C. under nitrogen. Finely divided potassium cyanide (102 parts) is added in one portion. The mixture is stirred three hours at between 40 and -30 C. and is then filtered cold under nitrogen. The filtrate is diluted with 17,837 parts of ether. The crystals which form are collected on a filter under nitrogen. The product is then washed with 3568 parts of ether containing a small amount of tetracyanoethylene and is dried under reduced pressure. Light tan potassium pentacyanoethanide (209 parts, 58% yield) is obtained. It is identified by its infrared spectrum.

Anal.Calcd. for C N K: C, 43.50; H, 0.00; N, 36.20. Found: C, 42.54; H, 0.39; N, 36.46.

To illustrate the utility of the products of this invention as sources of cyanogen, sodium pentacyanoethanide is heated at 150 C. at which temperature it cleaves almost quantitatively into sodium tetracyanoethylenide and cyanogen gas. Potassium pentacyanoethanide when heated at 70 C. is similarly cleaved into potassium tetracyanoethylenide and cyanogen gas. None of the sodium or potassium salts of cyanoform or the sodium or potassium salts of tetracyanoethane yields cyanogen when heated.

When lithium cyanide, rubidium cyanide, and cesium cyanide are substituted for sodium cyanide in the procedure of Example III, there are obtained respectively lithium pentacyanoethanide, rubidium pentacyanoetha nide, and cesium pentacyanoethanide. Pentacyanoethane and its alkali metal salts represent a preferred group of the products of this invention because of their ready availability from the process of the invention.

As many apparently widely embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not limited to the specific embodiments thereof except as defined in the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A pentacyanoethanide of the formula wherein M is a cation selected from the group consisting of hydrogen ion, metal ions, ammonium, phenylammonium, diethylammonium, trimethylammoniurn, and trimethylsulfoniurn and x is an integer corresponding to the valence of M.

2. Compound according to claim 1, where M is an alkali metal.

4. NaC(CN) C(CN) 6. Process for the formation of wherein M is an alkali metal cation which comprises contacting an alkali metal cyanide with a molar excess of at least 0.01 mole of tetracyanoethylene at a temperature in the range from C. to room temperature and in the absence of molecular oxygen and isolating the resulting alkali metal salt of pentacyanoethane.

7. Process according to claim 6 wherein said temperature range is 100-0 C.

8. Process according to claim 6 wherein the reaction is carried out in the presence of an inert diluent.

9. Process for the formation of which comprises contacting NaCN with a molar excess of tetracyanoethylene in the presence of an inert diluent at a temperature in the range 100-0 C. in the absence of molecular oxygen.

References Cited in the file of this patent UNITED STATES PATENTS 2,809,972 Middleton Oct. 15, 1957 

1. A PENTACYANOETHANIDE OF THE FORMULA 